Public Policy Polling and Rasmussen Reports both conduct their polls using automated telephone surveys that use a technology known as Interactive Voice Response. In polling the Maine Senate race, both firms also asked only about King, Summers and Dill by name.

The firms differed, however, in sample size: Public Policy Polling surveyed 804 likely voters to Rasmussen’s 500. And the firms have differences when it comes to calculating results.

According to its website, Rasmussen “weights” results by political party, so if the percentage of respondents who say they are Democrats is greater than the percentage of voters registered as Democrats, the pollster adjusts results accordingly.

Thirty-five percent of Rasmussen’s respondents identified themselves as Democrats, 30 percent as Republicans and 35 percent as “other.” According to the secretary of state’s office, 33 percent of Maine’s voters were registered as Democrats, 28 percent as Republicans and 36 percent unenrolled in November 2011.

Public Policy Polling doesn’t adjust results based on party identification. In its survey, 42 percent of respondents said they were Democrats, 29 percent Republicans and 29 percent independents.

If Rasmussen’s Maine Senate survey leans Republican, the results could be good news for King, who has seen his lead shrink in the Senate race since June as outside groups with Republican ties have funneled nearly $2 million into ads attacking the former governor.

The Portland-based Maine People’s Resource Center also released a poll last week that showed King with 44 percent support, Summers with 28 percent and Dill with 15 percent. Seven percent were undecided, and a combined 6 percent chose independents Woods, Dodge or Dalton.

The resource center — which is affiliated with the left-leaning Maine People’s Alliance, a statewide advocacy group — didn’t weight results by political party and asked respondents about all six Senate candidates by name.